The present invention relates to an articulated industrial robot.
FIG. 1 shows a conventional articulated industrial robot. This conventional articulated industrial robot has an arm constituted by an upper arm 2 and a forearm 3. A driving source 3c for driving, through a feed screw mechanism, parallel link mechanism 3a, 3b connected to the forearm 3, is secured to a rotary support 1 such as a turret for rotatably supporting the upper arm 2. Also, a driving source for a feed screw mechanism for actuating a lever 2a unitarily connected to the upper arm 2 is secured to the rotary support 1, although it is hidden behind the driving source 3c and not shown in this figure. The arrangement is such that the power from a power source is converted into the movement of the forearm 3 through the action of the link mechanism 3a, 3b and feed screw mechanism.
FIG. 2 shows another type of conventional articulated industrial robot. This type of industrial robot has a forearm 3 adapted to be driven by a driving source which is secured to an upper arm 2', in such a manner that the forearm 3 is moved relatively to the upper arm 2. The later-mentioned type of conventional articulated industrial robot has an advantage that the mechanical restriction to the stroke or range of operation is small to afford a large stroke or range of operation over the first-mentioned type of known articulated industrial robot.
A wrist 4, having at least one degree of freedom, is secured to the end of the forearm 3 of each of the robots explained hereinbelow.
In the known articulated industrial robots, the driving source and the driving system for the upper arm 2" forearm 3', and the wrist 4 are arranged, for example, in a manner shown in FIG. 3. Namely, the upper arm 2" is rotatably supported at one end thereof by the rotary support 1 through the medium of a bearing 18. A driving source 6 such as a D.C. servo motor, for driving the upper arm 2", is secured to the rotary support 1. The torque of the driving source 6 is transmitted to a reduction gear 9, such as a harmonic reduction gear, through a rotary shaft 7 and a pair of bevel gears 8, 8', and the output side of this reduction gear 9 is connected to the upper arm 2". The forearm 3' is rotatably secured to the other end of the upper arm 2' through a bearing 19. A driving source 10, such as a D.C. servo motor for driving the forearm 3', is attached to the upper arm 2". The torque of this driving source 10 is transmitted to a reduction gear 13, such as a harmonic reduction gear, fixed to the upper arm 2", through a rotary shaft 11 and a pair of bevel gears 12, 12'. The output side of the reduction gear 13 is connected to the forearm 3'. The wrist 4 is rotatably secured to the end of the wrist 3' through bearings 20, 20', and is adapted to be driven by a driving source 14 such a D.C. servo motor attached to the forearm 3. The torque of this driving source is transmitted, through a rotary shaft 15 and a pair of bevel gears 16, 16', to a reduction gear (not shown), such as a harmonic reduction gear, the output shaft of which is connected to the wrist 4, to thereby drive the wrist 4. Although the wrist 4 is shown in FIG. 3 to have only one degree of freedom, i.e. the rotation around an axis A--A', the wrist 4, in an ordinary articulated industrial robot, has two or more degrees of freedom including a rotation around an axis B or a rotation or pivoting around a point C (shown by arrow C') in combination. In the articulated robot of the type shown in FIG. 3 in which the driving source 10 for driving the forearm 3' is secured to the upper arm 2", the driving source for achieving each of above-mentioned degree of freedom is secured to the forearm 3' as in the case of the driving source 14 shown in the drawing, and achieves rotary motion around its own axis of rotation by making use of a differential gear mechanism.
Namely, in the articulated robots of the types explained heretofore, the forearm 3 or 3' and the wrist 4 are driven independently relatively to the upper arm 2, 2' or 2" and the forearm 3 or 3', respectively, and the positions or postures of the forearm 3 or 3' and the wrist 4 are controlled through the control of their positions relative to the upper arm and the forearm, respectively. In other words, the posture of the wrist 4 is affected by the postures of the upper arm and the forearm. Therefore, in order to move the wrist 4 while maintaining the latter in a predetermined relation to an absolute reference plane such as floor surface, platform or the like, it is necessary to effect the control of the wrist 4 in such a manner so as to compensate for the change of postures of the upper arm and the forearm.
In practical use of the industrial robot, there are many tasks to be performed by the robot. Some of these tasks require complicated motion of the wrist 4, but there still are many types of tasks which require substantially linear motion of the wrist 4 in only one direction, e.g. assembling of parts, shifting of goods, packing and so forth, as well as tasks which require the wrist 4 to be maintained substantially in the constant posture in relation to the working surface, e.g. marking on a flat surface, application of an adhesive and so forth. The budget for automation of such comparatively simple tasks is usually limited. In the known articulated industrial robots explained hereinbefore, however, it is necessary to control the posture of the wrist 4 making use of the wrist driving source 14 in order to maintain the wrist 4 in a constant posture relative to the working surface, which, in turn, requires the wrist 4 to have the necessary degrees of freedom to meet the demands of complicated robot tasks. In these known articulated industrial robots, therefore, it is quite difficult to reduce the production cost of robot and to facilitate the control of the wrist by eliminating driving sources, driving system and controller which are unnecessary for the simplified robot tasks of smaller degree of freedom.
In addition, since the known articulated robots incorporated a plurality of driving sources for imparting to the wrist a plurality of degrees of freedom, as well as differential gear systems, the change in the degree of freedom of the wrist 4 cannot be achieved without being accompanied by a large scale of modification including the modification of construction of the forearm 3 itself. It is, therefore, extremely difficult to easily change the combination of degrees of freedom to meet various requirements or expected robot tasks.